Police were initially called out to the flat in Aberdeen due to concern for the man’s well-being.
But officers had to draft in specialist help from Scottish Fire and Rescue Service and paramedics after finding an unidentified material nearby.
The man was taken to Aberdeen Royal Infirmary for treatment while Scottish Fire and Rescue Service carried out tests to determine the nature of the substance.
A police spokeswoman said: “Police Scotland has assisted the Scottish Fire and Rescue Service (SFRS) following concern for a man in the Heathryfold area of Aberdeen.
“He has since been taken to Aberdeen Royal Infirmary.
“Police attended at a residential property in the Waulkmill Crescent area of Aberdeen at approximately 1:20pm after an unknown substance was found.
“SFRS is carrying out an assessment.
“There has not been any danger to the public during this incident.”
A spokesman for the Scottish Ambulance Service confirmed “a number of crews” were in attendance, including a special operations unit.
Four appliances from the Scottish Fire and Rescue Service were also called to the scene.
Firefighters set up an incident tent and could be seen wearing breathing apparatus as they carried out tests on the substance.